Refractory article for molten metal handling

ABSTRACT

An article suitable for contact with molten metal, comprising at least one wall formed from refractory material, the wall including a region having a thermal conductivity which is lower than that of the refractory material. The lower thermal conductivity region of the wall of the article may be an air-filled cavity in the wall, and the article may be a feeder sleeve.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is based on provisional application Ser. No. 60/168,745, filed Dec. 6, 1999.

BACKGROUND AND SUMMARY OF THE INVENTION

[0002] The present invention relates to the handling of molten metal, and in particular to articles formed from refractory material for use with molten metal. The invention especially relates to refractory articles (e.g. sleeves or boards) for providing feeders for moulds in which metal is cast, and to refractory linings for ladles or other molten metal handling vessels.

[0003] In the production of metal castings, it is usual to provide so-called “risers”, “feeder heads” or “feeders” (collectively termed “feeders” in the present specification) which contain a reservoir of molten metal to supply metal to the mould cavity in order to compensate for shrinkage of the metal in the mould cavity as it cools and solidifies. Feeders are positioned with respect to the mould cavity such that liquid metal contained in them is able to flow into the mould cavity under gravity, to replenish the mould cavity with molten metal during such shrinkage. Most feeders are in the form of sleeves formed from refractory material (i.e. material which is able to withstand the temperature of the molten metal being cast). Other feeders comprise boards which may be used in conjunction with other boards to form a feeder cavity, or they may comprise flexible or articulated boards which may be wrapped or otherwise manipulated to form feeder sleeves, for example.

[0004] In order to provide effective feeding of molten metal to a mould cavity as the metal in the mould cavity cools and solidifies, it is important for the metal contained in a feeder to remain molten for as long as possible. For this reason, conventional feeders are generally formed from heat insulating refractory materials, to maintain the temperature of the metal above its melting point for as long a period as possible. Some feeders additionally include materials which react exothermically during use (initiated by the heat of the molten metal) thereby generating their own heat.

[0005] When molten metal is handled, for example during production, treatment or casting, vessels, e.g. ladles or the like, which contain the molten metal are commonly lined with refractory material. Such refractory linings may comprise preformed shapes such as sleeves or cups, or they may comprise boards etc. As well as needing to withstand the temperature, pressure and chemical nature of the molten metal, and to protect the structure of the vessel itself (normally formed from metal, e.g. steel), refractory linings are often required to provide a degree of thermal insulation to retain as much of the heat of the molten metal as possible.

[0006] According to a first aspect, the present invention provides an article suitable for contact with molten metal comprising at least one wall formed from refractory material, the wall including a region having a thermal conductivity which is lower than that of the refractory material.

[0007] The article according to the invention is preferably a feeder article (e.g. a sleeve or a board), or a lining for a molten metal handling vessel (e.g. a ladle). However, the article may generally be substantially any refractory article intended to contact molten metal and for which thermal insulation may be advantageous.

[0008] The lower thermal conductivity region of the article preferably comprises a material having a lower thermal conductivity than that of the refractory material. Alternatively, the lower thermal conductivity region may comprise a vacuum (or at least a partial vacuum).

[0009] In preferred embodiments of the invention, the lower thermal conductivity region is located between at least two spaced apart portions of the refractory material of the wall. Most preferably, the lower thermal conductivity region comprises a cavity within the wall. The cavity may contain a lower thermal conductivity material, or it may contain at least a partial vacuum. The article may contain a single cavity or a plurality of such cavities. The or each cavity may be open to the environment, particularly, for example, for embodiments in which the cavity contains air. Alternatively, the or each cavity may be closed and therefore substantially isolated from the environment. In some embodiments of the invention, the article may include one or more cavities open to the environment and one or more cavities closed to the environment.

[0010] The cavity (where present) is preferably formed within a wall of refractory material which is formed as a single piece. Alternatively, the cavity may be formed by the joining together of two or more initially separate wall parts. For example, where the article is a sleeve, the sleeve may be formed by the joining together of a first sleeve with a second, larger, sleeve, such that the first sleeve is located within the second sleeve, with the cavity provided by a gap between the sleeves. The sleeves may be formed from the same, or different, material. For example, the material of one of the sleeves (normally the innermost sleeve) may include exothermic material whereas the outermost sleeve may comprise substantially no exothermic material. The article may comprise three or more sleeves joined together. Advantageously, the separate wall parts and/or sleeves may include connecting members for mechanically interconnecting the wall parts and/or sleeves together.

[0011] For embodiments of the invention which include a lower thermal conductivity material, the material is preferably a gas. The gas is preferably air, but other gases may be used, for example argon or nitrogen, or another inert gas. Mixtures of gases may be used.

[0012] Additionally or alternatively, the lower thermal conductivity material may be a solid. Preferred solid materials include foams, or fibrous materials, for example. The lower thermal conductivity region may additionally or alternatively comprise a region of refractory material having a lower density than that of the remainder of the refractory material of the wall. Advantageously, the lower thermal conductivity material may be material, preferably refractory material, which has been treated so as artificially to reduce its bulk density. This may be achieved, for example, by agglomeration of particles of the material to form low density porous agglomerates; alternatively, for example, the material may be mixed with a foaming agent to produce a setting foam.

[0013] In general, the greater the difference between the thermal conductivity (or thermal conductivities) of the refractory material and that of the lower thermal conductivity region of the wall of the article, the greater will be the benefit of the lower thermal conductivity region. It is preferred for the thermal conductivity (or thermal conductivities) of the refractory material(s) to be at least twice, more preferably at least three times, even more preferably at least four times, even more preferably at least five times, especially at least ten times, as great as the thermal conductivity of the lower thermal conductivity region. In other words, the thermal conductivity of the lower thermal conductivity region of the article is preferably at least an order of magnitude lower than that of the refractory material. For example, if the thermal conductivity region of the article comprises air or another gas, it may have a thermal conductivity of approximately 0.03 W/mK, whereas the refractory material may have a thermal conductivity of approximately 0.5 W/mK. Following the teaching of the present specification, the skilled person will be able to select the appropriate design and/or materials for the article.

[0014] As already indicated, the article of the invention preferably comprises a sleeve or a board. Where the article is a sleeve, the lower thermal conductivity region of the wall preferably extends around substantially the entire circumference of the sleeve. The lower thermal conductivity region of the wall preferably extends along substantially the entire length of the sleeve. If the lower thermal conductivity region is in the form of a cavity, the cavity preferably extends around substantially the entire circumference, and preferably along substantially the entire length, of the sleeve. The cavity may be continuous or discontinuous, i.e. it may comprise a single cavity or it may comprise a plurality of separate cavities.

[0015] Where the article is a sleeve, it will normally have a substantially circular cross-section, but other cross-sectional shapes are possible, including oval, or square, or rectangular, or another polygonal shape.

[0016] According to a second aspect, the invention provides a method of manufacturing an article according to the first aspect of the invention, comprising forming the lower thermal conductivity region of the wall of refractory material at the same time as the remainder of the wall is formed.

[0017] Preferably, the wall of refractory material is moulded or pressed or vacuum formed. In embodiments in which the lower thermal conductivity region comprises a cavity in the wall, in this aspect of the invention the cavity is preferably formed by means of one or more formers (for example pins or other structures) as the article is moulded or pressed or vacuum formed.

[0018] The lower thermal conductivity region may be formed by means of an insert around, or against, which the remainder of the wall of refractory material is formed. For example, the insert may comprise a preformed low density insulator. Additionally or alternatively the insert may comprise a hollow casing filled with a gas (e.g. air) or a low density material (e.g. perlite) or a sacrificial material (e.g. a polymeric foam). The insert may comprise a sealed pouch or bag filled with gas, e.g. a polymer bag or “bubble wrap”. Additionally or alternatively, the insert may comprise a structure, for example a framework, which provides enhanced structural strength to the sleeve or other article. The structure may have the form of a spiral, “waffle” or lattice shape, for example.

[0019] According to a third aspect, the invention provides a method of manufacturing an article according to the first aspect of the invention, comprising forming the lower thermal conductivity region of the wall of refractory material subsequently to the remainder of the wall being formed. For embodiments of the invention in which the lower thermal conductivity region of the wall comprises a cavity, the cavity is preferably formed by the removal of some of the material of the wall subsequent to the wall having been formed. For example, portions of the wall may be removed by drilling, machining, milling, or the like.

[0020] The lower thermal conductivity region of the wall of refractory material, or at least a part thereof, may, in some embodiments of the invention, be created only once the article is used with molten metal. For example, the lower thermal conductivity material may be provided by means of the incorporation into the refractory material of a sacrificial material which, during use at the elevated temperatures associated with the molten metal which the article contacts, changes its form to create the lower thermal conductivity region, or an even lower thermal conductivity region. For example, the sacrificial material may change its form by dissociation, vapourisation, or volatility, creating increased porosity in the refractory material, or even creating a cavity within the wall of refractory material.

[0021] The material from which the article is formed must be sufficiently refractory in order to withstand the temperature of the molten metal to be cast. Suitable materials include metals, ceramic materials, and cermet materials. Bonded particulate refractory materials such as sand, e.g. silica sand, bonded fibrous and/or microspherical refractory materials such as alumina or aluminosilicate may be used. For some applications, the article may also include exothermic materials, i.e. materials which will react exothermically during use. The skilled person will be able to select the appropriate refractory and/or exothermic materials according to each particular application.

[0022] As mentioned above, the article is preferably moulded or pressed or vacuum formed. A particularly preferred manufacturing process comprises partially drying (e.g. by means of a vacuum) a slurry (preferably an aqueous slurry) of particulate and/or fibrous materials together with a binder, on a former which produces the shape of the article. The partially dried and formed slurry is then preferably heated in order to remove the last traces of water or other solvent, and to cure or harden the binder.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention will now be described, by way of example, with reference to the accompanying drawings, of which:

[0024]FIG. 1 is a schematic illustration of a feeder sleeve according to the invention;

[0025]FIG. 2 is a schematic illustration of the feeder sleeve of FIG. 1, in longitudinal cross-section;

[0026]FIG. 3 is a schematic illustration of a refractory board according to the invention;

[0027]FIG. 4 is a schematic illustration of a quarter segment of a second type of sleeve according to the invention;

[0028]FIG. 5 is a schematic illustration of a quarter segment of a third type of sleeve according to the invention;

[0029]FIG. 6, views a and b, are schematic illustrations of a fourth type of sleeve according to the invention;

[0030]FIG. 7 is a schematic illustration of a quarter segment of a fifth type of sleeve according to the invention; and

[0031]FIG. 8 is a schematic illustration of a quarter segment of a sixth type of sleeve according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 shows a feeder sleeve 1 formed from refractory material. The sleeve 1 comprises a cylindrical wall 3. As shown in FIG. 2, the wall contains a cavity 5 which is itself cylindrical in shape, and extends within the wall around the entire circumference of the sleeve. The cavity, which is completely enclosed, is filled with air.

[0033]FIG. 3 shows a board 7 according to the invention. The board may be a feeder board or part of a lining for a molten metal handling vessel, such as a ladle. The board 7 contains a cavity 9 which is completely enclosed within the refractory wall 11 from which the board is formed. The cavity 9 contains air.

[0034]FIG. 4 shows a quarter segment of sleeve according to the invention which is similar to that shown in FIG. 1, the only substantial difference being that the sleeve of FIG. 4 is closed by an upper wall 13.

[0035]FIG. 5 shows a quarter segment of sleeve according to the invention which is similar to that shown in FIG. 4, the only difference being that the cavity 5 in the cylindrical sleeve wall 3 contains an insert in the form of a flexible polymeric bag containing perlite particles 15. (As mentioned previously, perlite is a low density refractory material.)

[0036]FIG. 6, views a and b, shows a quarter segment, and its corresponding three-quarter segment, of a sleeve according to the invention which has the same outward shape as the sleeves shown in FIGS. 4 and 5. In this case, however, the cavity 5 in the cylindrical wall of the sleeve contains a lattice-like framework of internal ribs 17, to strengthen the sleeve.

[0037]FIG. 7 shows a quarter segment of another type of sleeve according to the invention. In this case, the sleeve comprises an outer wall portion 19 formed from insulating refractory material, and an inner wall portion 21 formed from exothermic material. A cavity 5 is defined between the inner and outer wall portions.

[0038]FIG. 8 shows a quarter segment of a sleeve according to the invention which has a different construction. In this case, a main part 23 of the sleeve forms an inner wall portion 25, an upper wall portion 27 and a lower edge portion 29; an outer wall portion 31 is formed from a separate part attached to the exterior of the main part 23. 

What is claimed is:
 1. An article suitable for contact with molten metal, comprising at least one wall formed from refractory material, the wall including a region having a thermal conductivity which is lower than that of the refractory material.
 2. An article according to claim 1 , in which the lower thermal conductivity region comprises a material having a lower thermal conductivity than that of the refractory material.
 3. An article according to claim 1 or claim 2 , in which the lower thermal conductivity region is located between at least two spaced apart portions of the refractory material of the wall.
 4. An article according to any one of claims 1 to 3 , in which the lower thermal conductivity region comprises a cavity within the wall.
 5. An article according to claim 4 , in which the cavity contains at least a partial vacuum.
 6. An article according to claim 4 when dependent upon claim 2 , in which the lower thermal conductivity region comprises said cavity containing said lower thermal conductivity material.
 7. An article according to claim 2 or any claim dependent thereon, in which the lower thermal conductivity material is a gas.
 8. An article according to claim 7 , in which the gas is air.
 9. An article according to any one of claims 2 to 4 or 6 , in which the lower thermal conductivity material is a solid.
 10. An article according to claim 9 , in which the material is a foam.
 11. An article according to claim 1 or claim 2 , in which the lower thermal conductivity region comprises a region of refractory material having a lower density than that of the remainder of the refractory material of the wall.
 12. An article according to claim 11 , in which the lower density refractory material is contained in a hollow casing insert.
 13. An article according to claim 1 or claim 2 , in which the lower thermal conductivity region comprises a hollow casing insert containing a gas.
 14. An article according to claim 4 , in which the cavity contains a framework of ribs.
 15. An article according to any preceding claim, comprising a feeder article.
 16. An article according to any preceding claim, comprising a lining for a molten metal handling vessel.
 17. An article according to any preceding claim, comprising a sleeve.
 18. An article according to any one of claims 1 to 16 , comprising a board.
 19. A method of manufacturing an article according to any preceding claim, comprising forming the lower thermal conductivity region of the wall of refractory material at the same time as the remainder of the wall is formed.
 20. A method according to claim 19 , in which the lower thermal conductivity region of the wall comprises a cavity which is formed by means of one or more formers.
 21. A method of manufacturing an article according to any one of claims 1 to 18 , comprising forming the lower thermal conductivity region of the wall of refractory material subsequently to the remainder of the wall being formed.
 22. A method according to claim 21 , in which the lower thermal conductivity region of the wall comprises a cavity which is formed by the removal of some of the material of the wall subsequent to the wall having been formed.
 23. A method according to claim 21 , in which the lower thermal conductivity region of the wall is created during use once the article contacts hot molten metal.
 24. A method according to claim 23 , in which the lower thermal conductivity region of the wall is formed by a sacrificial material which, once the article contacts the hot molten metal, changes its form to create the lower thermal conductivity region. 